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Topic: Gravitational Assist (Read 8746 times)

All this talk about traveling to Gliese 581 has got me to thinking. The New Horizon probe, and other spacecraft, use gravitational assist flybys of Jupiter and other planets to gain speed. What are the theoretical limits to this sort of thing? How much speed could you pick up if you spent several years doing this before heading out of the solar system?

All this talk about traveling to Gliese 581 has got me to thinking. The New Horizon probe, and other spacecraft, use gravitational assist flybys of Jupiter and other planets to gain speed. What are the theoretical limits to this sort of thing? How much speed could you pick up if you spent several years doing this before heading out of the solar system?

it is a momentum exchange. Jupiter lost the same amount of momentum that PNH gained.

The problem is get back to Jupiter or any other planet after getting the assist. PNH wouldn't be able to do it again since it is going out of the solar system.

Yes, you must work the directions of the planetary motions in. And the effect is primarily in the ecliptic.

To reach Jupiter in the first place, the usual procedure may involve a swing past Venus, back past Earth and/or Luna, another swing past Venus, and off to Jupiter for the big boost. The mind fairly reels at the math overload, but every pass is a slingshot designed to boost the kinetic energy of the spacecraft.

Yes, you must work the directions of the planetary motions in. And the effect is primarily in the ecliptic.

To reach Jupiter in the first place, the usual procedure may involve a swing past Venus, back past Earth and/or Luna, another swing past Venus, and off to Jupiter for the big boost. The mind fairly reels at the math overload, but every pass is a slingshot designed to boost the kinetic energy of the spacecraft.

Not necessarily true. Depends on the launch vehicle. PNH. Pioneers 10/11, Ulysses and Voyager went "straight" to Jupiter. Galileo and Cassini did intermediate flybys because their LV didn't have enough performance for the given payload mass

Ah, those were the good old days! Use a big rocket, skip the Venus/Luna slingshots.

If Dr. Bussard's idea works out, we can forget all this slingshot nonsense, stop worrying so much about waiting until the planets line up favorably, and just get in the rocket and GO! Flash Gordon, watch out!

Ah, those were the good old days! Use a big rocket, skip the Venus/Luna slingshots.

You didn't read Jim's reply carefully enough. It is not just the size of the rocket that matters, it's the size of the payload. The Titan IV rocket that required gravitational assists to get Cassini to Saturn was in fact more powerful than the Titan III rockets that sent the Voyagers directly to Jupiter. The gravity assists were required because Cassini was quite a bit heavier than the Voyagers.

Going back to the "good old days" requires smaller spacecraft, not bigger rockets. New Horizons is a good example of this; it was able to do a direct approach to Jupiter because it was quite a bit lighter than Cassini.-- JRF

you could do a powered flyby around the sun, use jupiter to send your probe to a heliocentric orbit with a very low perihelion then apply a 10km/sec DeltaV, that should send you out of the solar system at around 100 Km/s, reaching alpha centauri in about 12,000 years.with high end chemical/low end nuclear propulsion that's as good as flybys get.of course your probe would need a heavy radiation/thermal shielding.

When a probe uses a gravity assist and takes a planets ( say Jupiter) gravity, does Jupiter eventually regain that lost "orbit" from when it slows down? if not, then we could theoretically send millions of Gravity Assist probes past jupiter and its rotation would slow drastically.

When a probe uses a gravity assist and takes a planets ( say Jupiter) gravity, does Jupiter eventually regain that lost "orbit" from when it slows down? if not, then we could theoretically send millions of Gravity Assist probes past jupiter and its rotation would slow drastically.

Sombody please correct me as i think i am wrong here.

Correct

it is a momentum exchange. The amount gained by the spacecraft is lost by the planet. But it is not the planet rotation that gravity assist affects, it is the orbit around the sun

When a probe uses a gravity assist and takes a planets ( say Jupiter) gravity, does Jupiter eventually regain that lost "orbit" from when it slows down? if not, then we could theoretically send millions of Gravity Assist probes past jupiter and its rotation would slow drastically.

Sombody please correct me as i think i am wrong here.

Correct

it is a momentum exchange. The amount gained by the spacecraft is lost by the planet. But it is not the planet rotation that gravity assist affects, it is the orbit around the sun

Thanks so much for clarifying that. I can now sleep at night knowing that The planets will never stop spinning, ( though they may someday become a fixed star in are sky some day,.. if humans still around that is.

When a probe uses a gravity assist and takes a planets ( say Jupiter) gravity, does Jupiter eventually regain that lost "orbit" from when it slows down? if not, then we could theoretically send millions of Gravity Assist probes past jupiter and its rotation would slow drastically.

Sombody please correct me as i think i am wrong here.

Correct

it is a momentum exchange. The amount gained by the spacecraft is lost by the planet. But it is not the planet rotation that gravity assist affects, it is the orbit around the sun

Thanks so much for clarifying that. I can now sleep at night knowing that The planets will never stop spinning, ( though they may someday become a fixed star in are sky some day,.. if humans still around that is.

Actually, because of the lost of momentum, the orbital energy around the sun is decrease and the planets's orbit is smaller and the periond decreases

I've not worked out the math myself, but Dr. Bussard once told me there is a second way to use a gravity well to pick up energy. If you've got to burn some rocket fuel anyway, and your trajectory takes you in to a gravity well, try to arrange to do your burns at or near the bottom, when your velocity is highest.

A given burn produces a specific delta-v. Do that delta-v at higher velocity and the kinetic energy gain is higher than if you do the burn moving slower out in flater space.

Slingshot maneuvers take advantage of the relative velocity of the object you're using to do it ... you're doing a direction change into the orbital direction of the that object to pick up speed. The Sun is pretty much stationary in reference to the rest of the solar system, so tends to be fairly useless for slingshots in the system. But it sits in a heckuva deep gravity well, and doing a burn close in to it may make sense, if your trajectory is going to take you there.